# Magnetic field and its affect on velocity

1. Jul 17, 2011

### evox

A researcher is interested in creating a particle accelerator that can spin particles in the uniform magnetic field at the high possible speed. This can be achieved by all of the following EXCEPT

A)increasing magnetic field strength
B) increasing mass of the particle
D)increasing charge of the particle

I understand that the answer is B. But i don't understand why A is not incorrect, since to my knowledge, increasing the strength of a magnetic field does not increase velocity, rather it decreases the orbital radius, since work is not done and therefore there is no change in kinetic energy.

I am assuming that this question is asking for how to increase speed. Since, if it was asking how to increase acceleration, then A would be also correct.
F = qvB = mv2/r
B = mv/qr

Thanks,

2. Jul 18, 2011

### tiny-tim

welcome to pf!

hi evox! welcome to pf!
you have a design for a particle accelerator, and you are thinking of changing it

A is leaving the radius the same and increasing the field strength …

for the same mass, that will increase the speed

(C is leaving the field strength the same and increasing the radius)